How Much Dermal Filler is Considered Too Much into One Area?

I keep reading about compromised vasucularity causing necrosis due to too much filler in one area. I want some in my cheeks and want alot of "pop" to my cheeks. Now I am concerned. I am wondering if this will harm me. Also I can see big blue veins where my marionette lines are. They expressed they want to do filler there..My large veins are right at the skins surface pretty much. How will avoid this large veign?